In the construction trade and in related fields, it is a constant requirement to position studs, posts, walls, partitions, beams, bolts and a variety of other building materials at predetermined and accurate distances from each other and in a straight line or coplanar to each other.
This requirement is generally satisfied by two separate operations employing two separate devices. Generally, the first step is to provide a straight line and this is accomplished by means of a conventional chalk string which is a length of chalk-receptive string contained on a spool within a casing and removable through a small eyelet or opening in the casing. The string is drawn out of the casing through the eyelet and against a piece of marking chalk, the chalk particles becoming trapped within the porous body of the string. The chalked string is fastened adjacent the surface to be marked, such as a floor, and is snapped against the surface to transfer some of the chalk to the surface to provide a straight chalk line on the surface corresponding, for instance, to the path of a wall to be constructed.
The next step employs a measuring device, such as a folding wooden ruler or a flexible, retractable metallic measuring tape. The measuring device is aligned with the chalk line and additional chalk marks are applied manually to the surface to indicate predetermined, accurately-spaced distances along the chalk line. In the case of wall studs, such marks generally are spaced from each other by exactly sixteen inches. A carpenter relies upon the manually-applied marks to indicate, for instance, the relative positions of studs which he erects as a support for a straight wall.
It has been proposed to combine both of these steps by applying over the chalk string a number of spaced narrow applications of paint to render said narrow spaced areas non-receptive to the marking chalk. Such a chalk string provides a continuous chalk line which is interrupted by narrow voids which are spaced from each other by predetermined distances. The disadvantages of such chalk strings are manifold. Firstly, such strings do not provide reliably-spaced indicia because the length of a string will vary to some extent with changes in temperature and humidity; string increases in length or stretches when under tension, and string increases in length and becomes weak after prolonged use. Secondly, such chalk strings provide narrow spaced voids or chalkfree areas which are difficult to locate along the chalk line unless they are fairly wide, in which case they do not provide an accurate measurement guide. Also, if the chalk line is weak in intensity and/or is inadvertently contacted, voids may appear in unintended areas to mislead the carpenter. In other words, a positive mark is more reliable than the absence of a mark. Furthermore, paint or other materials applied to the string surface can wear off, particularly under the effects of repeated transport of the string through the narrow eyelet provided on most casings.